This invention relates to a pressure image forming apparatus in which an image obtained by exposing to an original image is transfered under pressure.
An example of an image recording medium in which microcapsules containing a photosensitive composition are utilized is disclosed in Japanese Kokai No. 179,836/1982. This system has a substrate which carries capsules made of a synthetic polymeric resin and containing a vinyl compound, a photopolymerization initiator and a coloring precursor.
In an image recording method using this system, microcapsules are hardened by being exposed, and parts of the microcapsules which have not been hardened are ruptured by pressure to release the coloring agent precursor, thereby forming a color image. This method ensures that an image of a high quality can be obtained by a dry-type simple process, but this system suffers from a disadvantage in that the photosensitivity is much smaller as compared with a system which makes use of silver halide.
The present applicant has proposed, in the specification of Japanese Patent Application No. 117,089/1985, a novel recording medium which has a high photosensitivity and which makes it possible to obtain an image of a high quality by a simple dry-type process. This recording medium applies at least a photosensitive silver halide, reducing agent, polymerizable compound and a color image forming substance over a substrate, and at least the polymerizable compound and the color image forming substance consist of a photosensitive composition confined in common microcapsules.
An image recording method which makes use of the latter type of photo- and pressure-sensitive medium is disclosed in the specification of Japanese Patent Application No. 121,284/1985 filed by the same applicant. According to this method, the heat-developable medium is first exposed so that a latent image is formed thereon in conformity with the image to be recorded. This medium is thereafter heated for development so that the polymerizable compound in the area where the latent image exists is polymerized to produce a polymeric compound, thereby thermally setting the microcapsules. Then, the medium is superposed on an image receiving medium having an image receiving layer capable of receiving the color image forming substance, and is pressed to the image receiving medium so that at least part of the microcapsules having no latent image is ruptured so as to transfer the color image forming substance to the image receiving medium, thereby forming an image on the image receiving medium. In order to obtain a clear image when the image on the photo- and pressure-sensitive medium is fixed under pressure to the image receiving layer, it is necessary to uniformly press the photo- and pressure-sensitive medium to the image receiving medium under given conditions, ex. 30-60 kg./cm. and a substrate thickness of 60-120 .mu.m.
A pair of conventional sheet pressing rolls may comprise a hard plastic roll, a rubber roll, or a metal roll having a smooth surface, and a metal roll which faces the former and has the same smooth surface. In the case of pressing rolls having such smooth surfaces, a large degree of pressure on these surfaces is needed to break the microcapsules. To obtain a large pressure on the surfaces, an extremely large pressing force is needed. This results in the occurrence of creases, an increased weight of the apparatus, and difficulty in the formation of a pressure-transferred image of high definition.